Biogen Highlights Advances from Its Neurology Research Programs and
Portfolio of Innovative Medicines at AAN Congress

TECFIDERA® and TYSABRI®
Data Support Early Treatment to Improve MS Patient Outcomes

New SPINRAZA® Data Show Robust Efficacy and
Safety Across a Broad Range of Individuals with SMA

April 18, 2017 07:30 AM Eastern Daylight Time

CAMBRIDGE, Mass.--(BUSINESS WIRE)--Biogen
(NASDAQ: BIIB) will present data from its portfolio of treatments and
investigational therapies for people with serious neurological and
neurodegenerative diseases at the 69th annual meeting of the American
Academy of Neurology (AAN) in Boston (April 22-28, 2017). Platform and
poster presentations throughout the meeting will highlight Biogen
research, including:

New real-world evidence supporting TECFIDERA® (dimethyl
fumarate), the world’s most prescribed oral medicine for multiple
sclerosis (MS), and TYSABRI® (natalizumab), the only
high-efficacy treatment with more than 10 years of clinical
experience, which underscore the importance of early treatment for MS;

New data further demonstrating the clinically meaningful efficacy and
favorable safety of SPINRAZA® (nusinersen), the
first and only U.S. Food and Drug Administration (FDA)-approved
treatment for spinal muscular atrophy (SMA) in pediatric and adult
patients;

Results from the Phase 1b study of aducanumab, an investigational
treatment for early Alzheimer’s disease, previously presented in
December 2016.

“Biogen’s commitment to improving outcomes for people living with MS
spans more than two decades, during which time we’ve fundamentally
changed the treatment of the disease. We are now applying our expertise
in neurology to discover and develop new therapies to address some of
the most challenging and complex diseases of the brain,” said Alfred
Sandrock, executive vice president and chief medical officer at Biogen.
“The data from our MS, SMA and Alzheimer’s disease programs reflect our
desire to advance the understanding of these diseases and make a
meaningful difference in the lives of patients.”

Multiple Sclerosis Data Reinforce Benefits of Early, Effective
TreatmentBiogen offers one of the most robust portfolios
of MS medicines in the industry, with therapies to help manage relapsing
MS at every stage of the disease. New real-world data comparing
TECFIDERA to other oral MS therapies contribute to the body of evidence
that TECFIDERA has strong and sustained efficacy in patients early in
the course of the disease, such as in those who are newly diagnosed or
were previously treated with another disease modifying therapy. Data to
be presented at the meeting also support the early and continued use of
TYSABRI in appropriate patients with high disease activity.

New SPINRAZA Data Show Robust Efficacy and Safety Across Broad
Spectrum of Individuals with SMABiogen will present
multiple studies evaluating the safety and efficacy of SPINRAZA across
individuals who are most likely to develop SMA Types 1, 2 and 3. The
results contrast with the natural history of SMA, where individuals
experience a progressive decline in motor function and a failure to
achieve motor milestones after symptom onset. New end- of -study CHERISH
data in individuals with later-onset SMA (most likely to develop SMA
Type 2 or Type 3) will be presented during the Emerging Science Platform
session. In addition, new interim data from the NURTURE study will
assess the efficacy and safety of SPINRAZA initiated in pre-symptomatic
infants genetically diagnosed with SMA and the potential benefit of
early treatment initiation.

Data from Phase 1b Study of Aducanumab in Early Alzheimer’s DiseaseData
from a Phase 1b study of aducanumab, Biogen’s investigational treatment
for early Alzheimer’s disease, will be presented at AAN. These data were
previously presented at the Clinical Trials on Alzheimer’s Disease
meeting in December 2016. Aducanumab is currently being evaluated in two
global Phase 3 studies, ENGAGE and EMERGE, which are designed to
evaluate its safety and efficacy in slowing cognitive and functional
impairment in people with early Alzheimer’s disease. Aducanumab is
thought to target aggregated forms of beta amyloid, including soluble
oligomers and insoluble fibrils, which can form into amyloid plaque in
the brain of Alzheimer’s disease patients. For more information about
the Phase 3 studies, including information about participating centers,
visit www.ClinicalTrials.gov
(NCT02477800 or NCT02484547).

About BiogenThrough cutting-edge science and medicine,
Biogen discovers, develops and delivers innovative therapies worldwide
for people living with serious neurological and neurodegenerative
diseases. Founded in 1978, Biogen is a pioneer in biotechnology and
today the Company has the leading portfolio of medicines to treat
multiple sclerosis, has introduced the first and only approved treatment
for spinal muscular atrophy, and is at the forefront of neurology
research for conditions including Alzheimer’s disease, Parkinson’s
disease and amyotrophic lateral sclerosis. Biogen also manufactures and
commercializes biosimilars of advanced biologics. For more information,
please visit www.biogen.com.
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About TECFIDERA®TECFIDERA is an oral
therapy for relapsing forms of MS, including relapsing-remitting MS, the
most common form of MS. More than 240,000 patients have been treated
with TECFIDERA worldwide.1

TECFIDERA has been proven to reduce the rate of MS relapses, slow the
progression of disability, and impact the number of MS brain lesions,
while demonstrating a favorable benefit-risk profile in people with
relapsing forms of MS, notably newly diagnosed and early switch
populations. 2 In clinical trials, the most common
adverse events associated with TECFIDERA were flushing and
gastrointestinal (GI) events. Other side effects include a decrease in
mean lymphocyte counts during the first year of treatment, which then
plateaued, and liver function abnormalities, which resolved upon
treatment discontinuation. TECFIDERA is contraindicated in patients with
a known hypersensitivity to dimethyl fumarate or any of the excipients
of TECFIDERA. Rare cases of progressive multifocal leukoencephalopathy
(PML), a rare opportunistic viral infection of the brain which has been
associated with death or severe disability, have been seen with
TECFIDERA patients in the setting of prolonged moderate to severe
lymphopenia.

The efficacy and safety of TECFIDERA have been studied in a large,
global clinical program, which includes an ongoing long-term extension
study.

For additional important safety information, and the United States full
prescribing information, please visit www.tecfidera.com
or your respective country’s website.

About TYSABRITYSABRI is a disease modifying therapy (DMT)
approved in more than 80 countries including the United States, the
European Union, Canada, Australia and Switzerland. In the United States,
TYSABRI is indicated as monotherapy for the treatment of patients with
relapsing forms of MS. In the European Union, it is indicated as single
disease modifying therapy in adults with highly active
relapsing-remitting multiple sclerosis (RRMS) for patients with highly
active disease activity despite a full and adequate course of treatment
with at least one DMT or patients with rapidly evolving severe RRMS.
TYSABRI is proven effective, with 10 years of experience in treating
RRMS, and more than 167,000 people treated worldwide and 559,000
patient-years of experience.3

TYSABRI is a monoclonal antibody that selectively binds to α4-integrin
and is thought to interrupt the activity of inflammatory cells in MS
patients by blocking the interaction between α4β1-integrin and vascular
cell adhesion molecule-1. Disruption of these molecular interactions
prevents transmigration of leukocytes across the endothelium into
inflamed parenchymal tissue. The specific mechanism(s) by which TYSABRI
exerts its effects in MS have not been fully defined.

TYSABRI has advanced the treatment of MS patients with its proven
ability to slow the progression of disability, reduce relapse rates, and
impact the number of MRI brain lesions with a well-characterized safety
profile. Data from the Phase 3 AFFIRM trial, which was published in the New
England Journal of Medicine, showed that at two years, TYSABRI
treatment led to a 68 percent relative reduction (p<0.001) in the
annualized relapse rate when compared with placebo and reduced the
relative risk of disability progression by 42 to 54 percent (12-24-week
sustained respectively, both p<0.001).

TYSABRI increases the risk of PML, a rare opportunistic viral infection
of the brain which has been associated with death or severe disability.
Risk factors that increase the risk of PML are the presence of anti-JCV
antibodies, prior immunosuppressant use and longer TYSABRI treatment
duration. Patients who have all three risk factors have the highest risk
of developing PML. TYSABRI increases the risk of developing encephalitis
and meningitis caused by herpes simplex and varicella zoster viruses and
clinically significant liver injury has also been reported in the
post-marketing setting. Serious, life-threatening, and sometimes fatal
cases have been reported in the postmarketing setting in MS patients
receiving TYSABRI. Other serious adverse events that have occurred in
TYSABRI-treated patients include hypersensitivity reactions (e.g.,
anaphylaxis) and infections, including opportunistic and other atypical
infections. Clinically significant liver injury has also been reported
in the post-marketing setting.

The overall benefit-risk profile of TYSABRI remains positive. For
additional important safety information and the full United States
prescribing information which includes a full list of adverse events,
please visit www.tysabri.com or
your respective country’s website.

About SPINRAZA® (nusinersen)SPINRAZA
is being developed globally for the treatment of SMA. SPINRAZA was first
approved by the FDA on December 23, 2016 within three months of
regulatory filing. Biogen has also submitted regulatory filings in
Japan, Canada, Australia and Switzerland and plans to initiate
additional filings in other countries in 2017.

SPINRAZA is an antisense oligonucleotide (ASO) that is designed to treat
SMA caused by mutations in the chromosome 5q that leads to survival
motor neuron (SMN) protein deficiency. SPINRAZA alters the splicing of
SMN2 pre-mRNA in order to increase production of full-length SMN protein.4 ASOs
are short synthetic strings of nucleotides designed to selectively bind
to target RNA and regulate gene expression. Through use of this
technology, SPINRAZA has the potential to increase the amount of
full-length SMN protein in patients with SMA.

SPINRAZA is administered via intrathecal injection, which delivers
therapies directly to the cerebrospinal fluid (CSF) around the spinal
cord,5 where motor neurons degenerate in patients with SMA
due to insufficient levels of SMN protein.6

The most common adverse reactions reported for SPINRAZA were lower
respiratory infection, upper respiratory infection and constipation.
Serious adverse reactions of atelectasis were more frequent in
SPINRAZA-treated patients. Coagulation abnormalities and
thrombocytopenia, including acute severe thrombocytopenia, have been
observed after administration of some antisense oligonucleotides.
Individuals may be at increased risk of bleeding complications. Renal
toxicity, including potentially fatal glomerulonephritis, has been
observed after administration of some antisense oligonucleotides.
SPINRAZA is present in and excreted by the kidney.

For complete SPINRAZA United States prescribing information please visit www.SPINRAZA.com.

About AducanumabAducanumab (BIIB037) is an investigational
compound being developed for the treatment of early Alzheimer’s disease.
Aducanumab is a human recombinant monoclonal antibody (mAb) derived from
a de-identified library of B cells collected from healthy elderly
subjects with no signs of cognitive impairment or cognitively impaired
elderly subjects with unusually slow cognitive decline using
Neurimmune’s technology platform called Reverse Translational Medicine
(RTM). Biogen licensed aducanumab from Neurimmune under a collaborative
development and license agreement.

Aducanumab is thought to target aggregated forms of beta amyloid
including soluble oligomers and insoluble fibrils which can form into
amyloid plaque in the brain of Alzheimer’s disease patients. Based on
pre-clinical and Phase 1b data to date, aducanumab has been shown to
reduce amyloid plaque levels.

In August 2016 aducanumab was accepted into the European Medicines
Agency’s PRIME program. In September 2016 the FDA accepted aducanumab
into its Fast Track program.

Biogen Safe HarborThis press release contains
forward-looking statements, including statements relating to the
potential benefits, safety and efficacy of TECFIDERA, TYSABRI, SPINRAZA
and aducanumab, the potential impact of our programs, results of certain
clinical studies and real-world data. These statements may be identified
by words such as “believe,” “except,” “may,” “plan,” “potential,” “will”
and similar expressions, and are based on our current beliefs and
expectations. You should not place undue reliance on these statements or
the scientific data presented. Drug development and commercialization
involve a high degree of risk, and only a small number of research and
development programs result in commercialization of a product. Results
in early stage clinical trials may not be indicative of full results or
results from later stage or larger scale clinical trials and do not
ensure regulatory approval. Factors which could cause actual results to
differ materially from our current expectations include the risk that we
may not fully enroll our clinical trials or enrollment will take longer
than expected, unexpected concerns may arise from additional data or
analysis, including data, analysis or results obtained during our
clinical trials, regulatory authorities may require additional
information or further studies, or may fail to approve or may delay
approval of our drug candidates, or we may encounter other unexpected
hurdles which may be impacted by, among other things, the occurrence of
adverse safety events, failure to obtain regulatory approvals in certain
jurisdictions, failure to protect intellectual property and other
proprietary rights, product liability claims, third party collaboration
risks, and the other risks and uncertainties that are described in the
Risk Factors section of Biogen’s most recent annual or quarterly report
and in other reports Biogen has filed with the U.S. Securities and
Exchange Commission. Any forward-looking statements speak only as of the
date of this press release, and we assume no obligation to update any
forward-looking statement.